The invention relates to use of ultrasonic radiation at relatively low levels into living tissue, as for the non-invasive healing treatment of bone fractures, pseudarthroses and the like.
Duarte U.S. Pat. No. 4,530,360 describes a technique of treating bone defects of the character indicated using a pulsed radio-frequency ultrasonic signal applied via a transducer to the skin of a patient and directed to the site of the defect. The radio-frequency signal is in the range of 1.3 to 2 MHz, and it consists of pulses at a repetition rate of 100 to 1,000 Hz, with each pulse having a duration in the range 10 to 2,000 microseconds. The Duarte apparatus comprises a radio-frequency oscillator connected to a driver, and a pulse generator is arranged to control driver output in accordance with a preselected duration and repetition rate of bursts of radio-frequency oscillations in the driver output. A flexible radio-frequency cable connects driver output to a body applicator, in the form of a hand-held plastic tube, one end of which is closed to mount a piezoelectric transducer, in the form of a thin flat disc, excited for thickness resonance.
Necessarily, therefore, in the Duarte apparatus, the source of electrical energy is remote, as on a table top, and the flexible connection to the body applicator must, in use, always be electrically "live" and, therefore potentially hazardous. Also, for the power levels involved, and considering the fact that two or more transducers seldom can be found to resonate at precisely the same frequency, the radio-frequency must be pretuned to serve one and only one transducer. In other words, apparatus of the Duarte patent necessarily dedicates the remote signal-generating part of the system to the particular applicator. And any attempt to replace a damaged applicator must involve a retuning of the signal-generator to the newly substituted applicator.